Electronic devices often include multiple electronic components attached to a substrate, such as a printable circuit board (PCB), which provides a base to support the electronic components, including integrated circuits, electronic subassemblies, capacitors, resistors and similar devices. PCBs also provide connection paths to electrically connect components to form electrical circuits which enable functioning of an electronic device. Electronic components attached to a PCB are likely to electrically short or malfunction after brief exposure to liquids or moisture. More specifically, exposed metal areas having voltage differentials in close proximity can easily experience short circuit events when corrosion or water immersion bridges the gap between such areas.
Conventional techniques for making electronic devices water-resistant or waterproof typically involve a cover placed on or around an electronic device housing after the electronic device has been assembled. These conventional techniques provide numerous shortcomings, such as lack of protection from accidental liquid encounters when not in place, failure to provide device protection from solid particles (e.g., dust) when not in place, bulky form factors that reduce device functionality, failure to provide device protection if not installed correctly by an end user, disabling functionality and accessibility of device ports such as a headphone jack or power connector, and so forth.
Other conventional techniques involve water-resistant surface treatments applied to electronic devices. One example of a conventional water-resistant surface treatment includes applying a polymeric coating formed by exposing the electronic device to static or pulsed plasma for a sufficient period of time to allow a polymeric layer to form on the surface of the electronic device. In another example, a coating comprising halo-hydrocarbon polymers is applied on a PCB and a board assembly by plasma etching, plasma activation, plasma polymerization and coating, and/or liquid-based chemical treatment. In yet another example, waterproof bulk conformal coatings are used in automotive electronic assemblies, and parylene films can be used to coat small devices, such as hearing aids using a highly reactive vapor phase precursor generated by pyrolysis of a solid.
However, conventional techniques for water-resistant surface treatments applied to electronic devices are not without limitations. First, surface treatment-induced high impedance, open circuit, or intermittent function of movable electronic contacts result in both component- and system-level functional failure of the electronic device. Additionally, plasma processing of a fluorohydrocarbon precursor often results in low process yields because fluorohydrocarbon molecules are large, unable to diffuse through a reticulated structure of substrate assemblies of electronic devices, and molecular fragments created by the plasma processing do not readily wet the surfaces of substrate assemblies, thus preventing complete encapsulation of the substrate assemblies. Further, electronic devices have interconnects, such as board-to-board (BTB), zero insertion force (ZIF) connectors, universal spring contacts, pogo pin contacts, dome switch assemblies, SIM and SD card readers, and so forth.
Failures of these interconnects typically results from contamination of an electrical contact zone in an interconnect from application of a water-resistant surface treatment, or mechanical disruption of the water-resistant surface treatment due to mechanical shock or mechanically disconnecting the interconnect during device rework. Interconnect failures are especially prevalent when the water-resistant surface treatment is a film with a thickness greater than 500 nm, and large molecular weight films such as parylene and cross-linked fluroacrylates. These conventional techniques thus require compromises to a film's water resistance or laborious masking of contacts, and result in significant reduction in achieved water resistance, increasing manufacturing complexity and cost, and ultimately do not provide the intended goal of waterproofing or sufficiently water resisting electronic devices.